The Army is worried that America is getting too out of shape to fight.

The lack of fitness in America's youth has been a problem for the military for years. According to a recent study by the Heritage foundation, more than 70 percent of Americans between the ages of 17 and 24 are ineligible to serve for some reason — and for many, it comes down to their physical fitness level.

For those who do make the cut, poor fitness can quickly lead to injuries during training — particularly among recruits from the Southern U.S., one of the most fertile recruiting grounds for the military. To fix this, the army wants to "fundamentally change the culture of fitness in the military," according to a new report by the Fayettville Observer.

But what exactly does what does it take to be combat ready, and how should the Army fix its fitness problem? To find out, we asked a couple guys who'd know — two former Army Rangers who've been through the harshest training the Army has to offer.

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"Most sergeants I know would probably agree that the kids are out of shape, because that's what older sergeants have been saying for, like, centuries," Adrian Bonenberger, who served in the army as an airborne Ranger-qualified infantry officer from 2005 to 2012, told MensHealth.com.

Randy Collins, a former Ranger-qualified First Sergeant and instructor at the Army's Ranger School, told Men'sHealth.com that part of the problem is that the Army Physical Fitness Test is a "poor assessment tool." The APFT, as it currently exists, is just a certain number of push-ups, sit-ups, and a two-mile run, usually administered every six months.

"Though I understand the reason behind it, the APFT is a very simple tool that is outdated," Collins said. When a doughy, 18-year-old recruit comes into basic training, Collins says, "It takes many months to get that soldier into fighting shape. You have to incorporate speed, strength, agility, load-bearing fitness, and mental fitness into your training."

"The APFT is a very simple tool that is outdated."

Other military officials told the Observer that soldiers often just train to ace the APFT, which can lead to overtraining injuries and doesn't actually prepare them for what they'll need to do in combat.

In fact, Bonenberger and Collins both noted that the actual demands of combat can't entirely be judged on a person's ability to crank out push-ups and sit-ups.

"The most important part of 'Army fitness' is actually mental endurance," Bonenberger said. "Much of the training that goes into shaping young soldiers and officers is conditioning them to push through pain and stress.

"Having incredibly fit soldiers simply isn't that important, on a certain level," he added. "In the infantry, you just need soldiers who can walk carrying lots of weight over long distances, and then shoot a rifle or machine-gun when they get to wherever they're going."

"The most important part of 'Army fitness' is actually mental endurance"

It looks like the military's new test might be a bit closer to this. The Observer reports that officials are experimenting with a new test, the Soldier Readiness Test, which incorporates more combat-applicable exercises — similar to this advanced training we witnessed in 2012. Soldiers would have to do a 225-pound tire flip, an agility test, a 240-pound dummy drag, a sandbag toss over a 7-foot wall, stack sandbags, and run a mile and a half, all while wearing their boots, combat uniform, and full body armor.

Michael McGurk, director of research and analysis directorate at the U.S. Army Center for Initial Military Training, recently told Men's Health about a different proposed new fitness test that would measure many more athletic qualities than the APFT.

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But Collins isn't convinced that setting arbitrary benchmarks is the best way to evaluate combat readiness. The SRT, he pointed out, would require specialized equipment — not every base has 225-pound tires lying around — and some of the exercises could expose soldiers to more injuries.

"There is no way to prepare for the conditions of combat except combat itself," he said. "You can't prepare to pull yourself up over a wall with all your gear on after a 30-hour patrol with no sleep except to be in that moment and succeed. You can train to get close, but never 100%."